Deathfire touch unintended refreshing.

I played anivia with deathfire touch, I noticed one thing, when I used my E when enemy got hit from my ult afterwards ticks got reducted to 1 second instead of still having deathfire touch procs from E (about 2 additional seconds in that situation), it overrides other spells that give more ticks. I this really intended? I actually don't believe that it is how it supposed to. It shoudn't punish you because you used additional skill.